Method and apparatus for eliminating tire droop



M. CLAPP Dec. 24, 1968 METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP 7Sheets-Sheet 1 Filed July 17, 1967 p00,? APT R 2 WW ;u WWW M M W I o w A0&24, 1968 M. CLAPP 3,418,400

METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP Filed July 17, 1967 7Sheets-Sheet 2 INVENTOR.

6f 44AM [MW maul/M4 M. CLAPP Dec. 24, 1968 METHOD AND APPARATUS FORELIMINATING TIRE DROOP 7 Sheets-Sheet 5 Filed July 17, 1967 I N V E NTOR. /Al/F/[E Jaw flea $24 Dec. 24, 1968 M. CLAPP 3,418,400

METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP Filed July 17, 1967 v 7Sheets-Sheet 4 I NVENTOR. MAW/ 5 IMP? M. CLAPP 3,418,400

METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP Dec. 24, 1968 7Sheets-Sheet 5 Filed July 17, 1967 Dec. 24, 1968 M. CLAPP 3,418,400

METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP I Filed July 17, 1967 7Sheets-Sheet 6 Anna/5K5 Dec. 24, 1968 M. CLAPP 3,418,400

METHOD AND APPARATUS FOR ELIMINATING TIRE DROOP Filed July 17, 1967 7Sheets-Sheet 7 United States Patent 3,418,400 METHOD AND APPARATUS FORELIMINATING TIRE DROOP Maurice Clapp, 1709 Rossmont, Redlands, Calif.92373 Continuation-impart of application Ser. No. 544,180, Apr. 21,1966. This application July 17, 1967, Ser. No. 660,549

19 Claims. (Cl. 26436) ABSTRACT OF THE DISCLOSURE A tire retreadingapparatus employs a counterbalance to carry the weight of the ramassembly used to draw the tires beads together during the insertion ofthe tire into a lower mold matrix. Before the beads are drawn together,the tire is supported around its periphery along the parting surface ofthe lower mold matrix. As the beads are being drawn together, thecounterbalance floats its carried weight and by a shift of load from theparting surface to the ram assembly allows the tire to seat in the lowermatrix.

Cross reference to related applications This is a continuation-in-partapplication of application Ser. No. 544,180, filed Apr. 21, 1966, andnow abandoned.

Background of the invention This invention relates to the art of tireretreading and, more particularly, to an apparatus and method for thehandling of tires to be retreaded in such a manner that the problem ofoff-center treads is eliminated.

The construction of modern automobile and truck tires has presentedserious problems for tire retreaders. One of the most serious of theseproblems is in the production of ofl-center treads by the retreadingprocess. An off-center tread is produced 'when the tread molded onto atire is oft-center relative to the center plane of the tire. Thisasymmetrical condition results from supporting the tire only along itsbeads prior to its insertion into the lower mold matrix of a vulcanizingapparatus. So disposed, the unsupported weight of the bulk of the tiretogether with the weight of the accessory apparatus used in theretreading process distorts the tire by causing axial displacement ofthe tread relative to the tires beads. This problem is especiallyserious with two-ply and low-profile tires. In two-ply tires there is avery light sidewall which is incapable of supporting the weight of thetire and the retreading apparatus used. Low profile tires have an extralarge cross section which concentrates the tires weight in its treadsection. In short, the added weight or limited stiffness of todayssidewalls causes tire droop which, unfortunately, persists throughoutthe retreading process.

In greater detail, the prior art retreading process which is responsiblefor the off-center tread condition is commenced by removing the oldtread rubber to expose the tires carcass. A band of unvulcanized rubber,which ultimately becomes the new tread, is cemented around thecircumference of the carcass. The carcass and cemented rubber band arethen prepared for the vulcanization process. The mold halves or matricesused in this process include ridges which define the finished tirestread pattern. These matrices must be undersized relative to the carcassand cemented rubber strip. The undersized matrices require a reductionin the diameter of the tire prior to its placement in the matrices.After a curing rim and an inflatable air bag are placed inside the tirescarcass, the tire diameter reduction step is accomplished by engaging apair of bead clamping members on the beads of the tire and drawing themembers together with the carcass 3,418,400 Patented Dec. 24, 1968spaced above the lower matrix of an open tire mold. This process,especially when used on two-ply and low-profile types, results in theaxial displacement of the tires tread relative to its normal orsymmetrical center plane by creating the condition which produces theoff-center treads. In short, tread misalignment is produced by allowingthe tires carcass together with the added weight of the air bag andcuring rim to remain unsupported during the diameter reduction processand before placement in the lower mold matrix. Once the droop or saggingcondition exists, it is not overcome by the subsequent support of thetire in the lower mold matrix. With a displaced tread during the moldingprocess, a reconditioned tire will be unbalanced and wear unevenly.

Summary of the invention The instant invention provides a simple andeffective apparatus and method for overcoming the off-center treadproblem and an improved method and apparatus generally applicable in theretreading art.

Briefly, the invention adds to the prior art retreading apparatus meansfor supporting the peripheral or outer circumferential edge of the tireto be retreaded before and during the tires reduction in diameter andplacement in the lower mold matrix. In addition, the transfer in theload felt by the peripheral support means to the head support orclamping members which occurs as the tire is being reduced in diameteris used to activate means for lowering the tire into the lower moldmatrix. The tire lowering means preferably utilizes a counterbalancewhich is sensitive to the transferred forces acting through the clampingmembers but which counteracts the weight forces of these clampingmembers and their associated apparatus which would otherwise distort thetire.

In greater detail, the invention contemplates the support of the outercircumferential edge of the tire on the parting surface of the lowermold matrix. The ram assembly used to draw the tire beads together issupported in a floating condition by the counterbalance. As the beadsare drawn together by the action of the ram assembly on the beadclamping members, the load supported by the parting surface is graduallytransferred to the ram assembly and, hence, the counterbalance. With theincrease in load, the counterbalance allows the ram assembly and itscarried clamping members to gradually lower the tire into the matrix.The ram assembly is preferably in the form of a fluid actuated pistonand cylinder combination with a shaft attached to the piston. The shaftengages the upper bead clamping member and, upon application of fluidpressure on the piston, forces the cooperating bead clamping membersclose together. The initial support of the tire on the parting surfacemay be accomplished in two ways. Initially, the lower mold matrix may becarried by a mounting plate which is vertically positionable withrespect to the ram assembly. In its lower position, the mounting platefrees the lower mold matrix from the ram assembly in order to mount thetire in the bead clamping members prior to its reduction in diameter.Alternately, the ram assembly may be made vertically positionable withrespect to a fixed lower mold matrix to allow for tire mounting in thebead clamping members. The stationary lower mold matrix embodiment ispreferred when large tires are to be retreaded because the great weightof large mold matrices renders the positioning of the ram assembly moreeconomical and practical. In either case, the lower mold matrix or theram assembly is preferably positioned by a second ram assembly of one ormore pistons and cylinders which are operable to engage and correctlyposition their carried structure.

A tire to be retreaded is initially supported along its periphery by theparting surface of the lower mold matrix. As the tires diameter isreduced by the drawing together of the bead clamping members, the loadcarried by the lower mold matrix is transferred to these members. Theload on the bead clamping members is carried by the counterbalance whichpositions the beads of the tire and lowers their position as the load onthe counterbalance increases. As the load originally supported by themold matrix is transferred to the counterbalance, the tires peripherylowers into the mold matrix in unison with the tires beads. The supportprovided by the lower mold matrix insures that the vulcanization processis initiated with the tire in a symmetrical condition. The gradual shiftof load from the matrix to the counterbalance and the correlation ofthis shift to bead position maintain the symmetrical condition. Inshort, the initial support of the periphery of the tire and theutilization of the load transferred from the initial support to thecounterbalance to lower the tire into the lower mold matrix eliminatethe problem of olf-center treads.

These and other features, aspects and advantages of the instantinvention will become more apparent from the following description,appended claims and drawings.

Brief description of the drawings FIGURE 1 is a cross-sectionalelevation view of apparatus according to the prior art;

FIGURE 2 is a cross-sectional elevation View of one embodiment of thepresent invention;

FIGURE 3 is a cross-sectional elevation view of the apparatus shown inFIGURE 2 illustrating the terminal stages of process of this invention;

FIGURE 4 is a cross-sectional elevation view of another embodiment ofthe apparatus of this invention upon which the method of the presentinvention may be practiced;

FIGURE 5 is a cross-sectional elevational view of still anotherembodiment of the instant invention;

FIGURE 6 is a cross-sectional elevational view of the embodiment shownin FIGURE 5 with the tire in place in the lower matrix half;

FIGURE 7 is a cross-sectional elevational view of the embodiment shownin FIGURES 5 and 6 after the tire has been vulcanized;

FIGURE 8 is a cross-sectional elevational view of still anotherembodiment of the present invention; and

FIGURE 9 is a cross-sectional elevational view of the embodimentillustrated in FIGURE 8 illustrating the method of the presentinvention.

Description of the preferred embodiments FIGURE 1 shows a prior arttread centering device 10 hoses from a compressor 16 via a 4-portcontrol valve 17 which is operable to supply the high pressure air toeither end of the cylinder. The cylinder is slidably mounted in avertically bored boss 18 of a mounting plate 19. The mounting plate issupported on legs 20.

A lower mold matrix 21 is mounted on mounting plate 19 concentric to thevertical line along which shaft 14 and cylinder 12 are movable. Thematrix defines an upwardly open, annular mold cavity 22 concentric tothe ram. Matrix 21, in cooperation with a similarly configured,downwardly open, upper mold matrix (not shown, but see my prior Patent2,948,924), comprises a retread mold which, when closed, encompasses thetread of a tire to be retreaded and exposes the beads of the tire. Bothmatrices are equipped with means for heating a tire engaged therein tovulcanize new rubber to the carcass of the tire to be retreaded, and formolding a desired tread design into the new rubber; the tread design isdefined by ridges (not shown) extending into the mold cavity from thematrices.

In accord with the tire handling procedures practiced prior to thedevelopment of the present invention, cylim Cir der 12 is shown inFIGURE 1 to be positioned so that its upper end is disposed above matrix21. A lower bead clamping member 25 is fixed to the upper end of thecylinder concentric to piston shaft 14. The lower clamping member has anupwardly open groove 26 about its circumference. The groove isconfigured to receive the lower bead 27 of the carcass 28 of a tire 29to be retreaded. Shaft 14 passes through a central bore 30 in beadclamping member 25 and through a central bore 31 in an upper beadclamping member 32 engaged on and supported by the upper head 33 of thetire. Bead 33 is engaged in a downwardly open, circumferential groove 34in the upper clamping member. The upper clamping member is secured frommovement upwardly relative to shaft 14 by a pin 35 passed through theshaft and engaged with the upper surface of the clamping member.

Carcass 28 has secured to it a band 36 of new unvulcanized rubber. Theband is cemented to the circumference of the carcass after the old treadmaterial has been removed from the carcass. The carcass with band 36attached, however, is too large in diameter to fit into matrix 21. Thus,after an inflatable air bag 37 and an annular curing rim 38 have beendisposed in the carcass in the relation illustrated, the carcass isengaged between the bead clamping members in the manner described andthe clamping members are moved together by operation of ram 11 to causethe beads to move together. As the beads are moved together, thediameter of the tire (the diameter of the tire being measured in ahorizontal plane) is reduced until the carcass, with band 36 attached,can be fitted into mold cavity 22. In the prior art tire handlingprocedures, the beads are closed while the tire is supported abovematrix 21. After the tire has been positioned in the matrix, the air bagis inflated.

It is desired that tire 29 maintain a symmetrical shape relative to aplane (see line 40 in FIGURE 1) passing horizontally through the tiremidway between beads 27 and 33 as the beads are closed. However, wherethe carcass is of lightweight construction or where band 36 is verythick, the carcass is not able to support the Weight of itself and ofthe air bag and curing rim disposed in the carcass. Thus, incross-section as shown in FIGURE 1, the tire droops or sags relative tothe clamping members so as to have an asymmetrical cross-sectionalconfiguration wherein the centerline (see line 41 in FIGURE 1) of thetread is disposed below the plane 40. The tire maintains this asymmetryas the beads are closed. The band of new rubber is thus unevenlystressed and, when the tire is cured in the mold, the tread molded intothe new rubber will be off-center relative to the beads when the tireisremoved from the mold.

Two different stages of tire handling utilizing the method and apparatusof the present invention are shown in FIGURES 2 and 3. There isillustrated the inventive tire centering device which is similar todevice 10 shown in FIGURE 1 except that cylinder 12 of ram 11 is mountedon a carrier plate 51 and suspended from mounting plate 19 by aplurality of tension springs 52. Springs 52 collectively have a springconstant such that they float tire 29 on lower mold matrix 21 before andduring performance of the process of drawing the beads of the tire closetogether; that is, the springs 52 provide a counterbalancing force toabsorb the load which would otherwise act on the beads of a tire. Thesprings have a stiffness selected to allow the tire to move downwardlyinto contact with the matrix until the matrix carries that portion ofthe weight of the tire, the air bag and the curing rim which causes thetire to droop or sag into the asymmetrical cross-sectional tireconfiguration illustrated in FIGURE 1. The springs support the remainingweight of the tire, the air bag, and the curing rim and all the weightof bead clamping members 25 and 32, and ram 11; this avoids distortionof the tire which would otherwise be produced it the collective weightof these items were allowed to act through clamping members,

and 32 while the periphery of the tire was supported by the partingsurface 43 of mold matrix 21.

The practice of the method is commenced by disposing tire 29, with thedeflated air bag 37 and curing rim 38 inserted therein, on the lowermold matrix 21 concentric to the axis of the mold cavity 22. The tirebeads at this point are engaged between clamping members 25 and 32 intheir normal or expanded condition. This array is accomplished by firstsupporting the tire On the lower matrix 21 followed by the engagement ofthe clamping members 25 and 32 with the beads. Alternatively, thiscondition can be achieved by setting the tire on the lower clampingmember 25 when the latter is positioned above the lower matrix 21 andthen placing the upper clamping member 32 on shaft 14 in engagement withbead 33 allowing the springs 52 to attain an initial equilibriumcondition with the tire supported on the matrix 21 as described. Ineither case, the result is that the periphery of the tire is supportedon matrix 21 without sag relative to its beads and the tread centerline41 is coincident with plane bisecting the space between the beads.

Next, ram 11, comprising selectively operable means connected to thebead clamping members for moving the tire beads close together to reducethe diameter of the tire, is operated to cause the bead clamping membersto be moved together. As the beads are moved together and the diameterof the tire is reduced, the line of contact between the tire and thematrix moves radially outward relative to the tire (inwardly relative tothe matrix 21). The portion of the weight of the tire and its associatedapparatus which is carried by springs 52 is increased and the springselongate proportionally. Thus, the bead clamping members 25 and 32, andthe ram 11 are moved downwardly an amount related to the reduction oftire diameter. The tire, however, is supported during this operation sothat it does not sag relative to its beads and a symmetrical tirecross-sectional configuration is maintained.

FIGURE 2 shows tire 29 initially supported on matrix 21 at the junctionbetween an upwardly opening parting surface 43 of the matrix 21 and itscavity 22. During the initial stages of tire diameter reduction, thetire will be supported on the matrix along this line. As diameterreduction continues, the tire will begin to enter the mold cavity 22with the surface of the cavity supporting the periphery of the tire andthe tire floated relative to the matrix in order to prevent tiredistortion. Normally, however, when the diameter reduction processreaches a given point, the tire attains suflicient rigidity to resistthe sagging moment placed on th tire by the weight of the carcass, theair bag, and the curing rim; but because of the constant contact by themold surface, this rigidity factor need not be relied upon.

The process of reducing the diameter of the tire and lowering the tireinto the matrix progresses until the tire is seated in the matrix asshown in FIGURE 3. Thereafter the air bag is inflated, the mold isclosed, and the tire is cured.

After the tire has been cured, the tire is removed from the matrix, and,after the tire is positioned above the matrix, the clamping members aremoved apart and the retreaded tire is removed from device FIGURE 4 showsa tire centering device which is similar to device 50 except that aninflatable bladder 61 is provided to support ram 11 relative to matrix21. The bladder is engaged between the lower end of cylinder 12 and afloor 62 below boss 18 of mounting plate 19. The bladder is connected tocompressor 16 via an air hose 63 and a three-part rotary plug valve 64.The bladder is inflated so that it supports the tire in the same manneras do springs 52 of device 50. As the ram is operated and more and moreof the weight of the tire is borne by clamping members 25 and 32, theair in bladder 61 is compressed and the ram moves downwardly an amountrelated to the amount the tire is reduced in diameter. If desired, acompression spring having a selected spring constant equal to the springconstant of the system of springs 52 may be used instead of bladder 61.

FIGURES 5, 6 and 7 illustrate a preferred form of the apparatus of theinstant invention which is especially suitable for automobile tires. Thedifferences between the device 70 and the embodiments previouslydescribed reside in the use of a counterweight 78 as thecounterbalancing means for the axial load placed on the beads of thetire and the provision of a movable mounting plate 79. Thecounterbalancing means is provided by counterweight 78 attached by acable 84 to a lever 81 which in turn is pivoted at point 80 on frame 71.At the other end of the lever 81 is a cable 83 attached to extension 85through pin 82. As before, the counterweight 78 and its attendantapparatus are disposed in relation to the ram 11 and clamping members 25and 32 to offset the loads which would otherwise be carried by the beads33 and 27 of tire 29.

The use of a counterweight system is preferred because of the inherentease of its use, reliability, sensitivity to load changes, and ease ofadjustment of compensate for differences in expected loads. The mountingplate 79 has an axially bored boss 18 which slidably receives cylinder12 of ram 11. Vertical movement is provided through the use of a pistonand cylinder combination 90, preferably operated in a standard mannerthrough the use of hydraulic pump 77. This combination comprisescylinder 76, piston 75, and rod 74 secured to mounting plate 79 asillustrated. Upward movement of the mounting plate 79 is arrestedthrough the provision of vertical stops 72 and downward movement isarrested through the provision of stops 73. Both stops are fixed toframe 71 as is cylinder 76. Downward movement of ram 11, through thetransfer of load from the parting surface 43 of the mold matrix 21 tothe ram 11, is terminated when carrier plate 51 contacts the frame 71.

As in the previously described embodiments, the complete retreadingapparatus is not shown, there being absent the complementary upper moldmatrix, which is adapted to cooperate with the lower mold matrix 21, andits attendant positioning and securing apparatus. With this absence inmind, the preferred manner for operating the inventive device 70 willnow be described. The lower mold matrix 21 and the mounting plate 79 arepositioned on lower stops 73 through the manipulation of the hydraulicsystem 77. Tire 29 is then positioned on the lower bead clamping member25. The lower mold matrix 21, which is carried by mounting plate 79, isthen raised to contact the periphery of the tire 29 (as illustrated inFIGURE 5) through fluid pressure acting on the bottom portion of thepiston 75 and cylinder 76. The weight of the tire with its attendantcuring rim 38 and inflatable bag 37 is then supported by the partingsurface 43 of the lower mold matrix 21. Through this support of tire 29,drooping or sagging is eliminated. Because at this point there isrelatively little if any load on the heads, the raising of the lowermold matrix 21 to support the periphery of the tire 29 may well unseatthe beads 27 from the lower clamping member 25 without deleteriouseffect to the finished retreaded tire.

After the lower mold matrix 21 is so positioned, the upper bead clampingmember 32 is inserted over shaft 14 and engaged on beads 33 of time 29.The clamping members 25 and 32 are then brought together throughoperation of the ram 11 in the same manner as illustrated in US. Patent2,948,924. As the clamping members 25 and 32 are brought together, thediameter of the tire 29 is reduced and the load supported by the moldmatrix 21 gradually shifts to the ram 11 through lower clamping member25 allowing the ram 11 to move downwardly with respect to the mountingplate 79 through the bore in its boss 18. With this movement, thecounterweight 78 moves up slightly.

Thus through this transfer of load, the tire is allowed to seat itselfproperly in the cavity 22 of lower mold matrix 21 as shown in FIGURE 6.The upper mold matrix is then placed in its proper position relative tothe tire 29 and the lower mold matrix 2-1, the clamping members areseparated, the inflatable bag 37 inflated, and the curing and retreading of the tire accomplished. After the tire has been retreaded, theclamping members 32 and are once again brought together to reduce thediameter of the tire and to free it from the mold matrices. With thereduction in tire diameter, the upper mold matrix is removed and thelower mold matrix 21 is lowered with respect to the tire and the ram 11.During this lowering, the frame 71 supports the ram 11 through carrierplate 51. This state is shown in FIGURE 7. The clamping members 32 and25 are once again separated and the tire removed from the device tocomplete the process.

FIGURES 8 and 9 depict an alternate preferred embodiment of thisinvention which is particularly useful in retreading truck tires.Because of the weight of lower mold matrices used in retreading trucktires, it is impractical to have a vertically movable mounting plate toposition the lower matrix relative to the tire. In this embodiment, therequired positioning of the tire is effected with a stationary lowermold matrix. Tire centering apparatus includes a ram assembly 102, tirepositioning assembly 104, a lower mold matrix 106, a frame 108 and loadcounterbalancing assembly 110. As in the previous embodiments, frame 108includes a mounting plate 111 which supports lower mold matrix 106.

Ram assembly 102 includes a cylinder 112 in which is disposed avertically movable piston 114. A shaft 116 is attached to piston 114 andfollows the latters movement. Cylinder 112 is capped at its top by acover 118 and at its bottom by a cover 120. Lower bead clamping member122 is attached to ram assembly 102 through tie bolts 124. Tie bolts 124secure bottom cover to lower bead clamping member 122. Ram assembly 102passes through cross member 125 of frame 108. Piston 114 and shaft 116are positioned relative to cylinder 112 by pneumatic pressure acting onone side or the other of piston 114. The pneumatic pressure is suppliedthrough a compressor 126. A line 128 communicates the outlet ofcompressor 126 to a three-position valve 130. Lines 132 and 134 extendfrom valve into the upper and lower chambers of cylinder 112respectively. Valve 130 is selectively operable to communicate the upperchamber and the lower chamber with compressor 126 as well as toterminate communication between the chambers and the compressor.

Tire positioning assembly 104 includes a pair of rams 136 and 138. Ram136 includes a cylinder 140, a piston 142 and a shaft 143. Shaft 143 issecured to piston 142 and moves vertically in response to verticalmovement of the piston within cylinder 140. Cylinder is attached toframe 108 by means which are not shown. Similarly, ram 138 is attachedto cross member 125 and includes a cylinder 144, a vertically movablepiston 146 and a shaft 148. Shafts 143 and 148 are capable of engaginglower bead clamping member 122 to position it vertically. With verticalpositioning of clamping member 122, ram assembly 102 moves an equivalentamount. The power to actuate rams 136 and 138 is provided by compressor126. The outlet of compressor 126 is in communication with a two-wayvalve 150 through a line 152 and through a pair of lines 154 and 156 tothe interior of cylinders 140 and 144. Valve 150 is operable tocommunicate both rams 136 and 138 with compressor 126 as well as toterminate such simultaneous communication.

As in the previously described embodiments, load counterbalancingassembly 110 supports the weight of the ram assembly responsible fordrawing a tires beads together and the unsupported weight of the tire, acuring rim and an air bag while the tire is being lowered into a lowermold matrix such as matrix 106. This assembly includes a pair ofcounterweights 158- and 160 which are attached to ram assembly 102through cables 162 and 164 at lug 166. Lug 166 is attached to ramassembly 102 on bottom cover 120. Proper cable orientation with respectto ram assembly 102 8 and counterweights 158 and 160 is provided bypulleys 168, 170, and 172 and 174. Pulleys 168 and 170 are attached toframe 108 while pulleys 172 and 174 are attached to cylinder 112 of ramassembly 102.

The operation of the embodiment of the invention illustrated in FIGURES8 and 9 will now be described with particular reference to FIGURE 9. Tofacilitate this description, FIGURE 9 depicts a tire 176 which includesa carcass 178 and a band of unvulcanized rubber 180 which has beencemented around the circumference of the carcass. An inflatable air bag182 is in tire 176 as well as annular curing rim 184. The tires beads,indicated by reference numerals 186 and 188, are engaged by lower beadclamping member 122 and a complementary upper bead clamping member 190.Locking ring 192 is secured to shaft 116 and retains upper bead clampingmember with shaft 116. During the mounting of tire 176 in the two beadclamping members, shafts 143 and 148 of rams 136 and 138 are in theirvertically extended position to carry lower bead clamping member 122,the tire, curing rim and inflatable bag, upper bead clamping member 190and ram assembly 102. Shafts 143 and 148 are maintained in theirextended position by air pressure acting on pistons 142 and 146 (seeFIGURE 8) supplied by compressor 126 through valve 150. After the tirehas been mounted, shafts 143 and 148 are allowed to return to theirinactivated position by bleeding the air in rams 136 and 138 toatmosphere. This inactivated position of the shafts is shown in phantomin FIGURE 9.

The removal of the support provided by shafts 143 and 148 allows ramassembly 102 and its carried weight, tire 176, upper and lower beadclamping members 190 and 122, curing rim 184 and bag 182, to betransferred to load counterbalancing assembly 110. Assembly 110 allowstire 176 to lower until the weight of the tire, curing rim andinflatable bag is borne by the parting surface of matrix 106 and thetire is symmetrically aligned with respect to its center plane.

After shafts 143 and 148 are returned to their lowered position and thetire, bead clamping members and ram assembly 102 have reached theequilibrium position with band 180 resting on the parting surface ofmatrix 106, shaft 116 of ram assembly 102 is lowered to draw beads 186and 188 together by drawing bead clamping members 122 and 190 together.The bead clamping members are drawn together by the action of pneumaticpressure supplied by compressor 126 through valve 130 and line 132 onthe upper surface of piston 114, As the beads are drawn together,progressively more and more of the weight originally carried by theparting surface of lower mold matrix 106 is transferred to ram assembly102 by virtue of the diameter reduction of tire 176 allowing thecollapsing tire to seat in the matrix. The final position ofcounterbalancing assembly 110, ram assembly 102 and lower bead clampingmember 122 is shown in phantom in FIGURE 9.

While the instant invention has been described with reference to certainpreferred embodiments, it is clear that those skilled in the art maywell provide minor deviations from the process and apparatus describedwithout departing from the spirit and scope of the appended claims.

What is claimed is:

1. In the art of tire retreading, an improvement in a tire retreadingapparatus of the type including a frame; a mounting plate supported bythe frame; a lower mold 'matrix supported by the mounting plate having amatrix cavity adapted to receive a tire when its beads are drawn closetogether, the lower mold matrix also having a parting surface; andmeans, including upper and lower bead clamping members, for drawing thebeads of the tire close together to reduce the tires diameter to allowthe tire to be received in the matrix cavity in preparation for itsretreading; the improvement comprising:

means, capable of cooperating with the lower bead clamping member andthe lower mold matrix when a tire is initially supported along itsperiphery by the parting surface of the matrix and along its lower beadby the lower bead clamping member, for lowering the tire into the matrixcavity while supporting the tire in at least a substantially symmetricalcondition, the lowering being in response to the increase in load on thelower bead clamping member produced as the diameter of the tire is beingreduced.

2. The improvement claimed in claim 1, wherein the lowering meansincludes a counterbalance operatively disposed such that the load on thetires beads is at least substantially offset by the counterbalance whenthe tires periphery is supported by the parting surface of the moldmatrix, the counterbalance being responsive to the increase in bead loadoccasioned by the reduction of the tires diameter to allow the tire tolower into the matrix cavity. 7

3. The improvement claimed in claim 2, wherein the mounting plate has avertically bored boss and the bead drawing means includes a fluidactivated piston and cylinder capable of cooperating with the beadclamping members to draw such members close together, the cylinder beingslidably received in the boss, and the counterbalance is capable ofcooperating with the cylinder such that the cylinder lowers in responseto the increase in bead load produced upon the reduction of the tiresdiameter.

4. The improvement claimed in claim 3, wherein the counterbalancecomprises a lever pivotally mounted on the frame and attached at one endto the cylinder, and a weight attached-to the other end of the lever.

5. The improvement claimed in claim 3, wherein the counterbalancecomprises at least one spring attached at its ends to the frame andcylinder.

6. The improvement claimed in claim 3, wherein the counterbalancecomprises an inflatable bladder,

7. The improvement claimed in claim 4, including, as an additionalelement, means for raising and lowering the mounting plate with respectto the frame, the cylinder and the counterweight.

8. The improvement claimed in claim 7, wherein the raising and loweringmeans includes a second fluid activated piston and cylinder with thesecond cylinder mounted on the frame and the second piston attached tothe mounting plate.

9. The improvement claimed in claim 3, wherein the mounting plate isfixed in stationary position with respect to the frame and includingmeans for raising the fluid activated piston and cylinder above thelower mold matrix to allow the mounting of a tire with its beads betweenthe bead clamping members and ejection of the tire from the lower moldmatrix after it has been retreaded.

10. The improvement claimed in claim 9, wherein the fluid activatedpiston and cylinder raising means includes a second fluid activatedpiston and cylinder with the second cylinder mounted to the frame andthe second piston coupled to the lower bead clamping member, the lowerbead clamping member being rigidly attached to the first mentioned fluidactivated cylinder.

11. A method for lowering a tire into a retreading mold matrix having adiameter less than the normal diameter of the tire, the methodcomprising the steps of:

supporting the periphery of the tire on the parting surface of thematrix; I

engaging the beads of the tire between a pair of bead clamping members;

drawing the clamping members and tire beads close together to reduce thediameter of the tire and to gradually shift the load supported by theparting surface of the matrix to the clamping members; and

lowering, by the shift in load, the bead clamping members and the tiredownwardly into the matrix cavity during the drawing together of theclamping members an amount related to the amount of reduction of thetire diameter such that the tire maintains a symmetrical cross-sectionalconfiguration and tire droop is substantially completely eliminated.

12. The method claimed in claim 11, including the additional step ofcounterbalancing the load on the tires beads, which load exists beforethe drawing step, such that such load is at least substantially offsetand the tire beads are at least substantially free of axial stress.

13. The method claimed in claim 12, wherein the counterbalance step isaccomplished through the use of a counterweight.

14. The method claimed in claim 11, including the additional step ofraising the matrix up towards the tire, after the latter has beenengaged by the bead clamping members but before the supporting of thetires periphery, until the parting surface of the matrix contacts theperiphery of the tire.

15. The method claimed in claim 12, including the additional step ofraising the matrix up towards the tire, after the latter has beenengaged by the bead clamping members but before the supporting of thetires periphery, until the parting surface of the matrix contacts theperiphery of the tire.

16. The method claimed in claim 12, wherein the supporting step isaccomplished by lowering the tire, after it has been engaged by the beadclamping members but before such members are drawn close together, untilthe tires periphery is supported on the parting surface of the matrix.

17. The improvement claimed in claim 3 wherein the mounting plate isfixed in a stationary position with respect to the frame, the cylinderis attached to the lower bead clamping member, and means is provided forraising the lower bead clamping member above the lower mold matrix toallow the mounting of a tire thereon and the subsequent ejection of thetire from the lower mold matrix after it has been retreaded.

18. The improvement claimed in claim 17 wherein the lower bead clampingmember raising means includes a second fluid activated piston andcylinder mounted on the frame in position to raise the lower beadclamping member.

19. The improvement claimed in claim 18 wherein the lower bead clampingmember raising means includes a shaft secured to the second piston inposition to urge against the bottom of the lower bead clamping member.

References Cited UNITED STATES PATENTS 2,110,293 3/1938 Fisher 18-182,559,119 7/1951 Frank 264-315 2,712,156 7/1955 Potter et al 18-182,948,924 8/1960 Clapp 18-18 3,131,243 4/1964 Fannen 18-2 X 3,184,7945/1965 Sherkin 18-18 3,216,701 11/1965 Badgett 18-18 X 3,240,653 3/ 1966Mattox et aal 18-18 ROBERT F. WHITE, Primary Examiner.

N. RUSHEFSKY, Assistant Examiner.

US. Cl. X.R. 264-326; 18-2, 18

